Incandescent lamp and method of manufacture



, I. BERLEC Mar ch 24, 1916 INQANDESCENT LAIIP AND METHOD OF MANUFACTUREmed Oct. 2. 19s? lnventov Ivan BeT'Lec by M l-hsA t t-ore United StatesPatent O 3,502,932 INCANDESCENT LAMP AND METHOD OF MANUFACTURE IvanBerlec, Wicklifie, Ohio, assignor to' General Electric Company, acorporation of New York Filed Oct. 2, 1967, Ser. No. 672,276

Int. Cl. H01k 1/28 I US. Cl. 313315 2 Claims ABSTRACT OF THE DISCLOSUREIn the manufacture of quartz incandescent lamps having integral endportions of the tungsten filament hermetically sealed through the quartzenvelope, refractory metal leadin wires or pins are first secured toterminal end portions of the filament which is then inserted into thequartz envelope with an end portion of the filament confined within anopen end portion of the envelope and the associated lead-in wireextending to the exterior, the said open end portion of the envelope isthen heated above its softening point and the said end portion of thefilament is also heated while maintaining an inert gas atmosphere aroundthe filament to outgas the surface thereof, and said end of the envelopeis then compressed to form a hermetic seal with the said end portion ofthe filament while simultaneously embedding, although not hermeticallysealing, the inner end of the lead-in wire and the terminal portion ofthe filament which is connected thereto, thereby anchoring the lead-in'wire in the seal and providing a nonincandescible current supplyconductor which also serves as a heatsink for the said terminal portionof the filament which is not hermetically sealed.

BACKGROUND OF THE INVENTION Field of the invention The invention relatesgenerally to electric incandescent lamps and more particularly totungsten filament incandescent lamps having envelopes of essentiallyfused silica or quartz glass. Still more particularly, the inventionrelates to the construction and manufacture of a hermetic seal andcurrent supply connection to the filament.

DESCRIPTION OF THE PRIOR ART Although not necessarily limited thereto,the invention has particular application to, and will be described withreference to, incandescent lamps of the halogen regenerative cycle typewherein a tungsten filament is hermetically sealed in a compact envelopeof fused silica which is heated to a relatively high temperature duringoperation, and which contains an inert gas filling together with a smallquantity of a halogen, particularly iodine or bromine or compoundsthereof. During operation of the lamp, tungsten vaporized from thefilament and normally deposited as a dark film on the envelope walls,reacts with the halogen to form a compound which migrates back to thevicinity of the filament where it is broken down to release the tungstenwhich is redeposited on the filament, and to also release the halogenwhich is then free to repeat the cyclic reaction.

In view of the very low coefiicient of expansion of fused silica orquartz, the provision of a hermetic seal of the current lead-inconductors requires the use of a molybdenum foil of small dimensionaltolerances in order to obtain a tight hermetic seal in the quartz and toprovide the necessary current carrying capacity. In some cases, the foilis a separate piece of ribbon having a lead wire welded to each endthereof, one wire extending to the exterior of the lamp envelope and theother to the interior where it is connected to one end of the filament.In other cases,

3,502,932 Patented Mar. 24, 1970 the foil is a rolled portion of amolybdenum wire. In either case, the foil is a relatively costly part ofthe lamp. Such foil type structures are used in lamps of thedouble-ended type wherein a tubular quartz envelope contains an axiallyextending filament and has pinch seals at respective ends thereof inwhich are hermetically sealed a foil and lead wires connected torespective ends of the filament. Such seals are also used in lamps ofthe single-ended type wherein the quartz envelope has a pinch seal atone end thereof through which are sealed both of the foil type lead-instructures at respective ends of the filament.

A construction and manufacture of lamps wherein the foil is eliminatedis disclosed and claimed in applications Ser. No. 601,930 to R. C.Millikan, now Patent No. 3,448,320, and Ser. No. 601,927 to R. C.Millikan and L. A. Osburg, now Patent No. 3,448,322, both filed Dec. 15,1966, and the disclosures of which are incorporated herein by reference.In accordance therewith, seals are made directly between portions of theincandescent filament and the quartz envelope by keeping the diameter ofthe tungsten filament wire at a value less than 0.004 inch, byoutgassing the filament wire prior to and during scaling to preclude thepresence of any adsorbed gas and by continuously flushing the filamentand the quartz during scaling to preclude the presence of any molecularor gaseous impurities evolved from either during heating to beinterposed between the quartz and the clean oxide-free tungsten filamentin the final seal. After the quartz has been collapsed or shrunkdirectly over end portions of the filament, the terminals or lead-inwires are attached externally by a brazing technique.

It may be here noted that in some cases in the past, the ends of thecoiled tungsten filament in tubular lamps have been pulled out to formstraightened leg portions which extended into the pinch seals atrespective ends of the quartz lamp envelope where they were welded tofoil portions of lead-in conductors. In such cases, the said foilportions constituted the usual hermetic: seal with the quartz.Therefore, no attempt was made in such cases to hermetically seal theembedded portion of the filament, nor was a hermetic seal obtainedinasmuch as the filament wire was usually of too large a diameter and,moreover, no particular precautions were taken to insure a hermetic sealin accordance with the disclosure of the aforesaid copendingapplications of Millikan, and Millikan et al. Actually, the straightenedfilament leg structure was employed in some cases to provide an internalfuse elfect, as in Patent 3,211,942 to E. H. Wiley, or in some casessimply as an economy measure whereby the usual relatively heavy innerlead-in wire could be eliminated because the coiled filament wasotherwise adequately supported.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide an improved construction and method of assembly of the directfilament seal which will retain the advantages associated withelimination of the foil but which will also eliminate the problem ofattaching the lead-in conductors externally to the sealed-in filament.

In accordance with the invention, the objects are achieved bypreliminarily forming an assembly of the filament with lead-inconductors of refractory metal and of materially greater cross sectionalarea than the filament connected electrically andphysically torespective terminal end portions of the filament. The filament is thendisposed in the quartz envelope which has a portion thereof softened andcompressed and hermetically sealed directly to an end portion of thefilament andalso compressed about, although not hermetically sealed to,the interconnected terminal end portion of the filament and theassociated inner end of the lead-in conductor, so that the said terminalend portion of the filament which extends beyond the hermetically sealedportion thereof serves, together with the lead-in conductor, as acurrent supply member, and the lead-in conductor serves as a heat sinkto prevent destructive overheating of the said terminal end portion ofthe filament upon flow of current therethrough.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the drawing is an elevationof an electric incandescent lamp comprising the invention;

FIG. 2 is an elevation, partly in section and on an enlarged scale,illustrating the assembly and manufacture of a lamp in accordance with apreferred embodiment of the invention;

FIG. 3 is a fragmentary elevation, at a still more greatly enlargedscale, of one end of the lamp and having a slight modification of thelead-in conductor; and

FIG. 4 is an elevation of a light source wherein the lamp unit of FIG. 1is enclosed in an outer bulb.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawing, the lamp illustrated therein is of the tubular double-endedtype comprising a cylindrical envelope 1 of essentially fused silicawhich may be a vitreous quartz or a material sometimes referred to as96% silica glass or Vycor, and which has a pinch seal portion 2 at eachend thereof. The envelope 1 contains a tungsten wire filament hereinillustrated as a helically coiled-coil 3 extending axially of theenvelope. The ends of the coiled filament 3 are stretched out to formend legs 4 of quite open pitch which extend into and are hermeticallysealed in the respective pinch seals 2. The stretched out turns shouldbe sufficiently apart so that softened quartz can readily be compressedbetween them, but need not be straightened out. Some springiness isbeneficial to accommodate the thermal expansion.

The extremities or terminal end portions 5 of the legs 4 areelectrically and physically connected, preferably by welding, to innerend portions of respective lead-in conductors 6 which are, together withterminal portions 5 of the filament, also embedded in the pinch seals 2although not hermetically sealed therein because of their relativelylarge size and diiferent coefficient of expansion than that of quartz.

The lead-in conductors -6 are of refractory metal, preferablymolybdenum, having a melt-ing point above the softening point of thequartz envelope and having a materially greater cross section-a1 areathan the filament wire. Other refractory metals which might be used forthe lead-in wires include tungsten, tantalum and platinum or alloysthereof. The said lead wires 6 may be of simple pinlike form although,if desired, the inner ends may be somewhat flattened as shown .at 7 inFIG. 3, for ease of welding and to provide a lateral deformation whichmay be used to more securely anchor the lead wire in the seal. The saidend 7 is not flattened to a degree even approaching the extremely thindimensions required to form a hermetic seal with the quartz. Thehermetic seal is formed between the quartz and the embedded portion oftungsten filament leg 4 located between the inner end wall 8 (FIG. 3) ofthe pinch seal and the edge 9 of the lead-in wire 6.

The terminal end portion 5 of the tungsten filament wire which isconnected to lead wire 6 and which is therefore not hermetically sea-ledin the pinch seal 2 due to the relatively large size of the associatedlead wire 6, is nevertheless protected 'from destructive overheating byvirtue of the heat sink effect of the lead wire 6 which extendsexteriorly of the pinch seal 2 as a nonincand-escible current supplyterminal for the incandescible filament 3.

'By way of specific example, the tungsten filament wire size of notgreater than 0.004 inch diameter is compatible with the manufacture of alamp of 100-watt size for operation at about 120 volts and which has atungsten filament wire of about 0.0025 inch diameter. In such a lamp ofthe form shown in FIG. 1, the main coiled-coil body portion of thefilament 3 may be about inch long. The quartz envelope 1 may be ofapproximately inch outside diameter, and may be filled with an inert gassuch as nitrogen, argon, krypton or xenon or mixtures thereof, and asmall quantity of halogen such as iodine or a bromine compound such ashydrogen bromide or a hydrocarbon compound of bromine.

The lamp filament and envelope may be assembled and sealed together onequipment similar to that, for example, shown in Patent 2,855,265 toFoote et a1. As shown in FIG. 2, the envelope 1 may be supported in thiscase by a quartz exhaust tube 10 which extends laterally from themidpoint thereof and is, in turn, supported in a chuck member 11 whichis mounted for vertical adjustment and for rotation about its axis, andis connected to a supply of inert gas.

The previously prepared assembly of filament 3 and rigid molybdenum leadwires 6 is threaded into the envelope 1 and is supported by a cap member12 which has an axial bore in which the upper lead wire 6 is receivedand held by a screw 13. The cap 12 has a reduced lower end portion 14which fits the interior of the envelope 1 so that the cap 12 rests onthe upper end of the envelope and effectively closes it off. The lowerlead wire 6 is pulled down to slightly stretch the coiled filament 3 andto insert the said lower lead wire 6 in an axial bore 15 in a chuck 16and is held therein in any suitable manner, for example by the lateralend portion of a spring-loaded finger member 17 which is located in acavity in the chuck 16 in a position to be retracted from or permittedto press against the lead wire 6 in cavity 15, all as more fullyexplained in the aforesaid Patent 2,855,265.

A flow of inert gas, such as argon, is then started through the chuck11, exhaust tube 10 and lamp envelope 1 to purge the envelope of airand-provide a protective nonoxidizing atmosphere about the metallicfilament 3 and lead wires 6, the gas escaping through the slight spacebetween the lower end of envelope 1 and upper surface of chuck 16.The-argon gas line may be at a pressure of about 3 /2 pounds per squareinch, for example, in making a lamp of the l00watt size referred toabove. The lower end of the envelope 1 is then intensely heated by apair of burners (not shown) to a temperature above the softening pointof the quartz envelope. The lower end or leg portion 4 of the filamentis heated to white heat (between about 17502200 C.) by radiation andconduction and convection of heat from the intensely hot envelope whichalso highly heats the gas flowing through the envelope, so that the saidfilament leg is kept clean and free of oxide and adsorbed gases.

The plastic lower end of the envelope 1 is then pinched by a suitablepair of jaws (not shown) to flatten it and hermetically seal therein thelower filament leg 4 and to also embed therein the inner (upper) end ofthe lower lead wire 6 and the attached extremity or terminal end 5 ofthe filament leg. The pinch seal 2 may be a simple flattened area or, asindicated in FIGS. 1 and 3, it may be of known I-shaped cross section.Immediately upon pinching of the envelope, a flow of nitrogen gas may bestarted through a passage 18 in chuck 16 and directed at the exposed endof lower lead 6 to protect it from oxidizing.

The envelope 1 and the chuck 11 are then raised, the cap 12 is removed,the envelope 1 and chuck 11 are rotated 180 degrees to invert theenvelope while continuing the flow of argon gas therethrough. Theassembly is then lowered, the then lowermost lead wire 6 is engaged inchuck 16, and the fusing and pinch sealing operation is repeated.

Subsequently, the envelope 1 may be exhausted, and the final fill gasand halogen added in known manner through the exhaust tube 10 which isthen tipped off or sealed as shown in FIG. 1. In the particular l00-wattlamp described hereinbefore, the gas filling may be krypton at apressure between about 2000 and 5000 torr with about 5-20% nitrogenadded to avoid arcing across the filament when lighted, and a smallamount of iodine may be added as described and claimed in Patent2,883,571 to Fridrich and Wiley.

The lamp shown in FIG. 1 may be provided with bases at respective endsthereof, for example as shown in Patent 3,001,096 to F. A. Mosby.

However, the lamp of FIG. 1 may also be mounted within an outer bulb inplace of the simple filament of conventional incandescent lamps toprovide a lamp of exceptionally high efiiciency and maintenance of lightoutput for a long, useful life. Such a lamp is shown in FIG. 4 where, byway of example, the lamp unit 1 of FIG. 1 has its lead wires 6 securedto respectively long and short rigid lead wires 20 and 21 which haveportions thereof hermetically sealed in the pressed seal portion 22 of aglass stem 23 which has its lower flared end sealed to a glass bulb 24which may be evacuated and filled with inert gas, such as nitrogen,through a conventional exhaust tube 25. The enclosure of the lamp unit 1in the outer bulb 24 has the additional advantage that the presence ofthe nonoxidizing gas filling in bulb 24 avoids the necessity of takingany precautions to avoid oxidation of the lead wires 6 and terminal endportions 5 of the filament 3. It will be understood that in the finishedlamp the bulb 24 is provided with a base (not shown) such as theconventional screw base for insertion in a conventional socket.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An incandescent electric lamp comprising a hermetically sealedenvelope of essentially fused silica, an incandescible filament oftungsten wire of a diameter not greater than about 0.004 inch supportedwithin said envelope and having a unitary integral seal portion at eachend thereof with a clean elemental tungsten surface extending into andhermetically sealed directly to and terminating within a compressed sealportion of the envelope, a refractory metal lead-in conductor ofmaterially greater cross-sectional area than the filament wire andhaving an inner end electrically and physically connected directly to aterminal portion of each said end portion of the filament which isfirmly embedded together with said inner end of the conductor directlyin the seal portion of the envelope without being hermetically sealedtherein and which extends as a current conductor beyond the hermeticallysealed portion thereof,

said seal portions at the ends of the filament being the sole hermeticseals for respective ends of the filament and associated lead-inconductors, said lead-in conductor serving as a heat sink for thefilament terminal portion connected thereto and emerging exteriorly ofsaid compressed seal portion of the envelope as a nonincandesciblecurrent supply terminal.

2. In the manufacture of an incandescent lamp comprising a hermeticallysealed envelope of essentially fused silica and an incandesciblefilament of tungsten wire of a diameter not greater than about 0.004inch supported within said envelope and having a portion at each endthereof hermetically sealed directly to and within a com pressed sealportion of the envelope, the method which comprises preliminarilyconnecting a terminal portion at each end of said filament electricallyand physically di rectly to the inner ends of respective refractorymetal lead-in conductors of materially greater cross-sectional areathan. the filament wire, disposing the filament within the envelope withan extended end thereof confined within an open end portion of theenvelope along with the associated inner end of the lead-in conductorwhich also extends exteriorly of the envelope, heating the said endportion of the envelope above the softening point thereof andsimultaneously heating the confined extended end of the filament whilemaintaining an inert gas atmosphere around the filament to outgas thesurface thereof and maintain it free of oxide, and compressing the saidend portion of the envelope to form a hermetic seal solely with theheated extended end of the filament and to embed and anchor therein theinner end portion of the lead-in conductor along with the associatedterminal portion of the filament which is connected thereto.

References Cited UNITED STATES PATENTS 2,276,218 3/1942 Lemmens 313-318X 2,855,265 10/1958 Foote et al. 316-31 3,270,238 8/1966 Mosby 313-315 XJAMES W. LAWRENCE, Primary Examiner R. F. HOSSFELD, Assistant ExaminerUS. Cl. X.R.

